repeat unit of celluloseCellulose is a polymer. Polymer means many unit of monomer. Here poly means mono and mer means unit. Many thousands units of glucose molecule are used to made it. To form one molecule of cellulose, 10000 molecules of glucose may need in a chain. Molecular arrangement can vary to leads the cellulose which is different types. To make up cotton fiber there are millions of molecules are needed. 
In 1838 firstly noted a common material of plant cell walls. Chemically it is known as complex carbohydrate which is composed of glucose units. To manufacture textiles, smokeless gunpowder, paper and pharmaceuticals are made from it.